Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare destructiveHint=true, readOnlyHint=false, and idempotentHint=false, so the safety profile is known. The description adds genuinely new information — the change only takes effect on restart — but omits the destructive mechanism: whether an existing variable is silently overwritten and whether the previous value is recoverable. There is mild tension between "create or update" (a naturally idempotent upsert) and idempotentHint=false, though that likely reflects version/restart side effects rather than a real contradiction.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

A single tight sentence with the core action front-loaded and no filler. It is efficient, though its brevity is also the source of the missing detail rather than a virtue in itself.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

This is a destructive, non-idempotent mutation with four undocumented parameters and no output schema. The description says nothing about overwrite semantics, permission requirements, secret handling, or what is returned, leaving too much for the agent to infer.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 0% across four parameters, so the description carries the full burden and does not meet it. It never explains the id parameter (the target scope), the key naming constraint, the value size limit, or most importantly the secret boolean, which materially changes how the stored value is treated.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb pair ("Create or update") and resource ("user environment variable"), so the agent knows this is an upsert of an env var. It does not distinguish itself from the sibling env_update, which overlaps in intent and would leave an agent guessing between the two.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The only usage-adjacent statement is "applies on next restart," which is a behavior note rather than selection guidance. There is no when-to-use, when-not-to-use, or comparison to env_update or env_list, so the agent gets no routing help.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.